This invention relates to a cylinder device for a disc brake as defined in the preamble portion of claim 1 and more specifically relates to an improvement in the assembly of a dust boot.
One example of a traditional disc brake device is disclosed in FIG. 9. This prior art comprises: a carrier 600 to be fixed on a stationary portion of a vehicle; a caliper 200 configured with an inboard actuating portion 210, an outer reaction leg 220 facing the actuating portion, and a bridge 230 extending between the actuating portion 210 and the reaction leg 220; a piston 300 slidably fit into a cylinder bore 211 formed in the actuating portion 210 of the caliper 200; an inner pad 100 urged to be pressed by the piston 300 and frictionally engaged with one side surface of a disc rotor D; an outer pad 110 urged to be pressed by the reaction leg 220 and frictionally engaged with the other side surface of the disc rotor D; and a dust boot 400 designed so that an intermediate flexible portion 430 thereof is received in a large diameter bore 213 stepped up from the cylinder bore 211 and surrounded by a peripheral portion 214 defining the large diameter bore 213. Thick ring portions 410, 420 of the dust boot 400 are fit respectively into an outer circumferential groove formed on the peripheral surface of the piston 300 and into an inner circumferential groove 212 formed on the inner circumferential surface located adjacent to the open end of the cylinder bore 211.
This type of disc brake device is configured to perform a braking action by use of a pair of pads 100, 110 to sandwich and press both sides of the disc rotor D in the axial direction. The dust boot 400 is designed to protect the slidable portion of the piston 300 in the cylinder bore 211 from intrusion of foreign matter.
A process of installing the piston 300 and the dust boot 400 in the caliper 200 is explained with reference to FIGS. 10(A)-(D).
As shown in FIG. 10(A), one thick ring portion 410 of the dust boot 400 is elastically connected with the periphery of the cup-like piston 300 at its bottom side. As shown in FIG. 10(B), the piston 300 with the dust boot 400 is to be held, by one hand, within the space defined by the actuating portion 210, the bridge 230 and the reaction leg 220 so that the bottom of the piston 300 faces the actuating portion 210. As shown in FIG. 10(C), the other thick ring portion 420 of the dust boot 400 is fit, by the other hand, into the inner circumferential groove 212 adjacent to the open end of the cylinder bore 211. As shown in FIG. 10(D), as the piston 300 is being forced into the cylinder bore 211, the one thick ring portion 410 is fit into the outer circumferential groove 310 on the peripheral surface of the piston 300.
The above-described conventional art has the following points to be improved.
In the conventional device, the installation of the dust boot 400 is manually performed, which makes the installation complex and requires considerable time. That is, in the process shown in FIG. 10(C), when the other thick ring portion 420 of the dust boot 400 is to be fit into the inner circumferential groove 212 which is positioned within the cylinder bore 211, the peripheral portion becomes an obstacle for fingers to be inserted, which specifically causes a problem in fitting the other thick ring portion 420 into the inner circumferential groove 212.
Because of the difficulty in installing the dust boot 400, it is possible that the piston 300 is forced into the cylinder bore 211 with the dust boot 400 not being installed properly, which may cause a damage to the dust boot 400.
The peripheral portion functions to protect the dust boot 400 against flying gravel during operation in a vehicle and to increase the strength of the connecting section between the actuating portion 210 and the bridge 230 of the caliper 200. However, the peripheral portion at the brake center side has no effect on the strength increase. In this respect, its portion is wasteful, thereby increasing the weight of the device.
It is an object of this invention to provide a cylinder device for a disc brake device, which facilitates the installation work of the dust boot 400 into the inner circumferential groove 212 of the cylinder bore 211 and removes the wasteful portion of the peripheral portion 214, thereby eliminating the problems such as a weight increase and reducing the weight of the caliper device.
This invention is based on the finding that the peripheral portion 214 at the brake center side has no effect with respect to the strength increase and has an effect for protecting the dust boot 400 against flying gravel during operation in a vehicle but mainly increases the weight of the device.
To this end the present invention provides a cylinder device as defined in claim 1. Preferred embodiments of the invention are defined in the sub-claims.